It looks like Valve is cracking down on cheaters on Steam immensely. GameZone reports that Valve has banned a total of 121,496 accounts under Valve Anti Cheat (VAC) this month- and there are still eight days to go before the month is up! So the number could actually well end up going up.
61,437 of those bans were issued on July 19 alone. An explanation propounded by GameZone for this abnormally high number of bans is that people bought games like Counter Strike during the Steam Sale (which ended earlier this month), and many then proceeded to cheat, triggering a new, massive wave of bans- which certainly sounds like a plausible explanation to me.
As a reminder, VAC bans are different from regular Steam bans. These bans are permanent, non-negotiable, and under no circumstances can they be reversed. If you are caught with a VAC ban, you could lose access to any purchases you made within your games, such as skins, hats, and the like.
The long and short of it is- stop cheating.